Structures of polymers made from single site catalysts

ABSTRACT

Copolymers of ethylene and alpha olefins that have been formed by the polymerization reaction in the presence of a single site catalyst, such as a metallocene, are used to form collapsible dispensing containers and/or components thereof. Blends of the copolymers with propylene polymers are disclosed and used to form a body wall layer or a collapsible dispensing container head having good bond strength with a body wall layer formed of an ethylene polymer. Methods for improving the adhesion between collapsible dispensing container components, such as between body wall layer formed of an ethylene polymer and another body wall layer formed of a propylene polymer, or between a body wall layer formed of an ethylene polymer and a collapsible dispensing container head formed of a propylene polymer, are also disclosed.

This application is a continuation of U.S application Ser. No.09/684,567, filed Oct. 6, 2000, now U.S. Pat. No. 6,511,568 which is acontinuation-in-part of U.S. application Ser. No. 08/488,151, filed Jun.7, 1995, now abandoned, which is a division of U.S. application Ser. No.08/082,226, filed Jun. 24, 1993, now abandoned. The contents of U.S.Ser. No. 09/684,567 is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Polymeric materials have many applications in packaging structures. Theyare used as films, sheets, lidstock, pouches, tubes and bags. Thesepolymeric materials may be employed as a single layer or one or morelayers in a structure. Unfortunately, there are countless polymericmaterials available. Furthermore, resin suppliers frequently have atendency to claim many more applications for a product than the productis actually suitable for. In addition, in view of the specializedapplications and processing problems that are encountered despite thesuppliers' claims, one skilled in the art can not tell whether aparticular resin will be suitable for an application unless tested.However, for various reasons there are frequently drawbacks to the useof many of these polymeric materials. For example, ethylene vinylalcohol is an excellent oxygen barrier material for use in packagingfood products. However, this polymeric material can be affected bymoisture that is present in the atmosphere or the packaged product. As aresult, it is frequently found that some polymeric materials are betterfor certain applications than others.

One area where there is a need for suitable resins in film applicationsis in the area of heat shrinkable films. Heat shrinkable polymeric filmsare commonly used in packaging meats, particularly primal meat cuts andother large pieces of meat. While this description will mainly detailthe usage of films for packaging meat and meat by-products, it will beunderstood that these films are also suitable for packaging a myriad ofother products, including food products, and non-food products, forexample, dentifrices, cosmetics and pharmaceuticals.

Some of the films embodying the present invention are intended to beused by meat packers in the form of heat shrinkable bags with one openedend, which bags are closed and sealed after insertion of the meat. Afterthe product is inserted, air is usually evacuated from the package andthe open end of the bag is closed. Suitable methods of closing the baginclude heat sealing, metal clips, adhesives, etc. Heat is applied tothe bag once sealing is completed to initiate shrinkage of the bag aboutthe meat.

In subsequent processing of the meat, the bag may be opened and the meatremoved for further cutting of the meat into user cuts, for example, forretail cuts or for institutional use.

Suitable shrink bags must satisfy a number of criteria. Many bag usersseek a bag that is capable of surviving the physical process of filling,evacuating, sealing and heat shrinking. For example, during theshrinking process great stress can be placed on the film by the sharpedges of bone in the meat. The bag must also have sufficient strength tosurvive the material handling involved in moving the large cuts of meat,which may weigh a hundred pounds or more, along the distribution system.Because many food products including meat deteriorate in the presence ofoxygen and/or water, it is desirable that the bags have a barrier toprevent the infusion of deleterious gases and/or the loss or addition ofmoisture.

Conventional packaging for many products has frequently been made ofmultiple layer films having at least three layers. These multiple layerfilms are usually provided with at least one core layer of either anoxygen barrier material such as a vinylidene chloride copolymer,ethylene vinyl alcohol, a nylon or a metal foil, preferably aluminum.Heat shrinkable meat bags, for example, have generally used vinylidenechloride copolymers. The copolymer of the vinylidene chloride may, forexample, be a copolymer with vinyl chloride or methyl acrylate.Collapsible dispensing containers in the form of tubes may or may notuse one or more foil layers. The foil layers in addition to supplying anoxygen barrier also provide the dispensing tube with “deadfold”, i.e.,the property of a collapsible dispensing tube when squeezed to remain inthe squeezed position without bouncing back. Collapsible dispensingtubes employing a foil layer are disclosed in U.S. Pat. Nos. 3,172,571and 3,347,419, the disclosures of which are incorporated herein byreference. However, collapsible dispensing tubes do not require a foillayer. They may employ only one or more layers of thermoplastic orpolymeric materials. Examples of such tubes are disclosed in U.S. Pat.Nos. 4,418,841 and 4,986,053, the disclosures of which are incorporatedherein by reference. Methods of making collapsible dispensing tubes arewell known and are disclosed in the above and other U.S. patents.Generally, foilless plastic tubes have a body wall which can be a singlelayer plastic sheet or film which can be extruded in tubular form andcut into desired lengths. Multilayer plastic sheet and film can be madeby lamination, including coextrusion coating, processes, or bycoextrusion processes such as cast coextrusion through a flat die, ortubular coextrusion through a tubular die. Single and multilayer sheetor film that has been cast or laminated typically is shaped about anelongated cylindrical mandrel and sealed to itself along a side seam toform a tubular body. Single and multilayer sheet or film that isrespectively extruded or coextruded through a tubular die can beextruded in near final dimensional and vacuum sized to final dimension.Single or multilayer sheet and film can be coextruded and blown as alarger tubular form, which can be cut lengthwise and formed into a tubeas would be a flat sheet or film. The formed tubular body wall is joinedto a head typically having a neck with a dispensing orifice, and ashoulder. One end of the tubular body is joined to the shoulder of thehead. The head can be preformed by compression or injection molding.Usually, the tubular body is inserted into a die and a head is injectionmolded onto the end of the tubular body such that the head and tubularbody are fused or bonded together. The die which forms the head can beone which is shaped to form a head having an integral cap having anintegrally formed hinge. Typically, the tube head is sealed by a cap,filled through the tube's lower open end, and sealed at that end. Whilecollapsible dispensing tubes are generally made as described above, somecollapsible dispensing tubes and some containers are made by anextrusion blow molding process in which a single or multilayer parisonor preform is extruded and then blown in a mold into the desired shapeof the finished container, for example, one having an integral bodywall, shoulder, neck and closed bottom. Some containers includingcollapsible dispensing tubes, are made by injection molding such thatthey have an integral body wall, shoulder, and neck which can have anintegrally formed hinge and cap, and an open bottom.

Outer layers of films and body walls of containers used in packagingfood products can be any suitable polymeric material such as linear lowdensity polyethylene, low density polyethylene, blends of thesepolyethylenes, and ionomers, including sodium and zinc ionomers. Suchionomers include Surlyn, ethylene vinyl acetate etc. In conventionalshrink bags, the outer layers are generally linear low densitypolyethylene or blends thereof. Suitable outer layers for meat bags aretaught by U.S. Pat. No. 4,457,960 to Newsome, the disclosures of whichare incorporated herein by reference.

While conventional films have been suitable for many applications, ithas been found that there is a need for films that, for example, arestronger and more easily processed than conventional films. In meatbags, there is a need for films and bags that have superior toughnessand sealability and the ability to undergo cross-linking without unduedeterioration. Thus, it is an object of the present invention to provideimproved structures, including single and multi-layer films, sheets,lidstock, and containers, for example, pouches, tubes and bags. Inparticular, there is a need for structures for use in shrink bagswherein the shrink bags are capable of withstanding production stressesand the shrink process.

It has also been found that there is a need for containers, for example,collapsible dispensing containers or tubes having good bond strengthbetween a propylene polymer layer or component and an ethylene polymercomponent. Thus, another object of this invention is to provide improvedpolymeric structures with improved bonding properties. For example, itis known that in the packaging industry, it has been difficult to bond astructure, such as a collapsible dispensing tube head or layer, orsimply a layer made of a propylene polymer, such as polypropylene or apropylene ethylene copolymer, directly to a structure, for example, alayer made of an ethylene polymer, for example, a low densitypolyethylene (“LDPE”). While it is known to add an ethylene polymer to apropylene polymer structure to improve adhesion to the ethylene polymerstructure, it has heretofore been necessary to add a major amount of theethylene polymer to sufficiently improve the adhesion. This has beenundesirable. In adding a major amount, the desired properties of thepropylene polymer have been significantly diminished. For example,collapsible dispensing tube heads having an integral flip top capintegrally joined to the head by a living hinge are usually made of apropylene polymer, e.g., polypropylene or a propylene ethylenecopolymer, because the material properties of the polypropylene permitthe hinge to be flexed repeatedly over time without cracking orbreaking. Adding a major amount of a polyethylene to the propylenepolymer employed to form the tube head to obtain satisfactory adhesionto a polyethylene body wall layer results in diminished hingeflexibility and/or early hinge failure. Further, since tube heads madeof propylene polymer heretofore could not be satisfactorily bondeddirectly to a collapsible dispensing tube body wall layer ofpolyethylene, the packaging industry has been limited in types of headsand head materials that can be employed, and in the types of body walllayer materials that can be bonded to propylene heads. It therefore is amain objective of this invention to provide good bonding of a structure,for example, a collapsible dispensing tube head, or a layer, comprisedof a propylene polymer, to a structure, for example, a tube body walllayer comprised of ethylene polymer.

Another objective of the invention is to provide a packaging structureor film having a layer of propylene polymer which can be, or which issatisfactorily bonded to a contiguous layer of an ethylene polymer.

Another object of the invention is to provide a container, for example,a collapsible dispensing container or a collapsible dispensing tube headcomprised of a propylene polymer, joined or which can be joined withgood bond strength directly to a structure, for example, a layer, or abody wall or side wall layer of a container or tube, where the layer iscomprised of a polyethylene.

Another object of this invention is to provide an above-mentionedcollapsible dispensing container or tube which does not stress crackbetween its first ethylene polymer body wall layer and its propylenepolymer head after the dispensing container or tube has been exposed tostress crack inducing agents.

Another object of the invention is to provide a collapsible dispensingcontainer or tube such as mentioned above, whose head has an integralcap joined directly to the head by an integral living hinge which canundergo 10,000 flexing cycles without undergoing stress fracture orfailure.

Yet another object of this invention is to provide a method forimproving the adhesion between the above-mentioned structures withoutthe use of an adhesive.

SUMMARY OF THE INVENTION

The structures of the present invention may be single or multilayerfilms, sheets, lidstock, pouches, containers, tubes and bags where atleast one layer contains a polymer, usually a copolymer, formed by apolymerization reaction in the presence of a single site catalyst suchas a metallocene. Examples of such a polymer are ethylene and propylenepolymers and copolymers thereof. One preferred copolymer is a copolymerof ethylene and an alpha olefin where such alpha olefin has a carbonchain length of from C₃-C₂₀. The structures of the present invention mayalso include blends of polymers and copolymers formed by apolymerization reaction with a single site catalyst or blends of apolymer and copolymer formed by a polymerization reaction with a singlesite catalyst and another polymeric material. Examples of suitablepolymers for blending include: high and medium density polyethylene(HDPE, MDPE), linear low density polyethylene (LLDPE), low densitypolyethylene (LDPE), ethylene vinyl acetate (EVA), ultra low densitypolyethylene (ULDPE or VLDPE), polypropylene (PP) and ionomers such asSurlyn.

The present invention may also be a multilayer structure of at least twolayers, or at least three layers wherein the core layer is a barrierlayer. In one embodiment of the present invention, there may be a firstouter layer of an ethylene or propylene polymer or copolymer formed by apolymerization reaction in the presence of a single site catalyst, abarrier layer and a second outer layer of a polymeric material. Thesecond outer layer may be an ethylene or propylene polymer or copolymerformed by a polymerization reaction in the presence of a single sitecatalyst or a layer of another polymeric material such as high densitypolyethylene, medium density polyethylene, linear low densitypolyethylene, ultra low density polyethylene, low density polyethylene,ethylene vinyl acetate, an ionomer or blends thereof. The first outerlayer may also be a blend of the ethylene copolymer with anothersuitable polymeric material such as described above. A preferred polymerformed by a single site catalyst is a copolymer of ethylene and an alphaolefin such as butene-1 or octene-1. Additional layers such as adhesivelayers or other polymeric layers may be interposed in the structurebetween one or both of the outer layers or on top of one or both of theouter layers. The structure of the present invention may be renderedoriented either uniaxially or biaxially and cross-linked by any suitablemeans, such as for example irradiation or chemical cross-linking.

The present invention includes a structure in the form of a collapsibledispensing container which can be in the form of a tube comprised of alayer of, or comprised of a polymer, usually a copolymer, formed by thepolymerization reaction with a metallocene catalyst system or with asingle site catalyst, for example, a metallocene. The polymer can be anethylene or propylene polymer. The layer can be a blend of said ethylenepolymer or copolymer with a polyolefin. The ethylene polymer can be acopolymer or interpolymer of ethylene and a C₃-C₂₀ alpha olefin. Theethylene polymer preferably is a copolymer of ethylene and butene-1,preferably a linear ethylene butene-1 copolymer. The polyolefin of theblend can be a propylene polymer which can be polypropylene, a propylenecopolymer, for example, a copolymer of propylene and ethylene, or aterpolymer of propylene, for example, an elastomeric terpolymer derivedfrom ethylene and propylene. The propylene polymer of the blend cancomprise a major amount, preferably about 70 to 90 wt. %, and theethylene polymer of the blend can comprise a minor amount, preferablyabout 10 to about 30 wt. %, of the blend. In a preferred blend, thepropylene polymer, for example, the elastomeric terpolymer of propyleneand ethylene, can comprise about 85 to about 90 wt. % of the blend, andthe ethylene polymer, for example, a copolymer of ethylene and an alphaolefin, can comprise about 10 to about 15 wt. %, of the blend. Apreferred propylene polymer of the blend can comprise a copolymer ofabout 75 wt. % polypropylene and about 25 wt. % polyethylene, based onthe weight of the copolymer. The propylene copolymer can have a densityof about 0.899 to about 0.903 g/cm³, a melt flow rate of about 2 g/10min and a DSC melting point of about 161° C. The copolymer of ethyleneand an alpha olefin, preferably a linear ethylene butene-1 copolymer,can have a melt index of about 3.5 to about 4.5 dg/min, a density ofabout 0.900 to about 0.905 g/cm³, and a DSC peak melting point of about92 to about 98° C.

The collapsible dispensing container or tube of the invention can have abody wall which is or includes a layer comprised of an ethylene polymer,sometimes referred to herein as a first ethylene polymer, and acontiguous layer comprised of a blend of a propylene polymer and anethylene polymer, sometimes referred to herein as a second ethylenepolymer.

The collapsible dispensing container or tube can be comprised of a headhaving a dispensing orifice and a shoulder, and a body wall layer joineddirectly to the head, the layer being comprised of a first ethylenepolymer, and the head being comprised of a blend of a propylene polymerand a second ethylene polymer. In these containers, the second ethylenepolymer of the blend is formed by the polymerization reaction with ametallocene catalyst system, or with a single site catalyst, forexample, a metallocene. The containers of the invention can have a bodywall layer comprised of a blend of about 85 to about 90 wt. % of apropylene terpolymer and about 10 to about 15 wt. % of the ethylenebutene-1 copolymer. In the blend of the container or tube head, thepropylene polymer can be a copolymer of about 75 wt. % polypropylene andabout 25 wt. % polyethylene, based on the weight of the copolymer, andcan comprise about 70 to about 80 wt. % of the blend, and the secondethylene polymer can be a copolymer of ethylene and an alpha olefin andcan comprise about 20 to 30 wt. % of the blend.

The present invention includes a method for improving the adhesionbetween a first layer comprising a first ethylene polymer and acontiguous second layer comprising a propylene polymer, or for improvingthe adhesion between a collapsible dispensing container or tube headcomprised of a propylene polymer and a collapsible dispensing tube bodywall layer comprised of a first ethylene polymer, wherein the method caninclude blending with the propylene polymer which is to form the secondlayer or the tube head, a second ethylene polymer formed by thepolymerization reaction with a metallocene catalyst system, or with asingle site catalyst, which can be a metallocene. The method can alsoinclude blending with the first ethylene polymer which is to form thefirst layer, a propylene polymer, sometimes referred to herein as asecond propylene polymer, formed by the polymerization reaction with ametallocene catalyst system, or with a single site catalyst, which canbe a metallocene. The preferred method comprises blending a secondethylene polymer with the propylene polymer which is to form the secondlayer, or the tube head.

In the structures, containers and methods of the present invention, thetube head can have an integral cap that is integrally joined to the headby a living hinge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view of a three layer structure of thepresent invention.

FIG. 2 is a vertical sectional view of a five layer film of the presentinvention.

FIGS. 3-6 are examples of the structure of metallocene catalysts used inthe polymerization of the polymer used in the structures of the presentinvention.

FIG. 7 is a vertical sectional view taken through a two layer film ofthe present invention.

FIG. 8 is a front elevational view, with portions broken away andportions in vertical section, of a collapsible dispensing tube of theinvention.

FIG. 9 is an enlarged view of encircled portion of the head and bodywall of the collapsible dispensing tube of FIG. 8.

FIG. 10 is a vertical sectional view, with portions broken away, of analternative collapsible tube of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The structures of the present invention include films, sheets, lidstock,pouches, containers, tubes and bags. These structures may be a singlelayer or multi-layer structure. The structures are comprised of polymersthat have been polymerized in the presence of a single site catalyst,such as a metallocene. A metallocene is a complex organometallicmolecule typically containing zirconium or titanium, with a pair ofcyclic alkyl molecules. More specifically, metallocene catalysts areusually compounds with two cyclopentadiene rings fixed to the metal.These catalysts are frequently used with aluminoxanes as a co-catalystor an activator. One suitable aluminozane is a methaliumoxane (MAO).Besides, titanium and zirconium, hafnium may also be used as the metalto which the cyclopentadiene is bonded. Alternative metallocenes mayinclude Group IVA, VA and VIA transition metals with two cyclopentadienerings. Also mono-cyclopentadiene rings or sibyl amides may alternativelybe in the metallocene instead of two cyclopentadienes. Other metals towhich the cyclopentadine may be attached may include the metals in thelanthanide series. FIGS. 3, 4, 5 and 6 show representative metallocenesthat are suitable single site catalysts.

While the reaction mechanism is not completely understood, it isbelieved that the metallocene, single site catalyst confines thecopolymerization reaction to a single site over the polymer thuscontrolling comonomer placement and side chain length and branching. Thecopolymers formed from metallocene single site catalysts are highlystereo regular products with narrow molecular weight distribution. Themetallocenes can be used to polymerize ethylene, propylene, ethylenicand acetylenic monomers, dienes and carbon monoxide. Comonomers withethylene and propylene include styrene, substituted styrene, vinyl,acrylonitrile, methyl acrylate, methyl methacrylate and 1.4-hexadiene.The metallocene single site catalysts are capable of producing isotacticpolymers and syndiotactic polymers, i.e., polymers in which thecrystalline branches alternate regularly on both sides of the back boneof the polymer. There are two general types of single site catalystreactions. The first are nonstereoselective catalysts reactions whichhave been developed by Exxon and Dow and which are used to make Exxon'sExact resins and Dow's CGCT resins. See FIGS. 3 and 4. The second typeof reactions are stereoselective catalysts developed by Hoechst and Finafor stereo specific polymerization particularly of polypropylene andother olefins such as butene-1, and 4 methylpentene-1. See, e.g., FIGS.5 and 6.

The ethylene alpha olefins polymerized by a single site catalyst havelow crystallinity and a density that ranges from 0.854 to 0.97 gm/cc.Although this density range is similar to conventional ethylenepolymers, i.e., LDPE, LLDPE and ULDPE, the polymers in the structures ofthe present invention have a narrow molecular weight distribution andhomogeneous branching. The molecular weight distribution of thepreferred polymers may be represented by the formula

MWD Mw/Mn=<2.5.

The preferred polymers can have a MWD of from about 1.97, morepreferably about 2.0 to about 2.2.

In addition, the melt processability of these polymers (I₁₀/I₂) has arange of about 5.5 to about 12 while conventional homogenous polymersare generally less than 6.5 at an MWD of 2. The melt tension of thesepolymers is in the range of about 1.5 to 3.5 grams.

The MWD of these polymers may be determined using a Water's 150 GPC at140° C. with linear columns (103₆A-10⁶ A⁰) from Polymer Labs and adifferential refractometer detector. Comparison of the MWD of a 1MI,0.920 density CGCT polymer with that of 1MI, 0.920 density conventionalLLDPE illustrates the very narrow MWD of the CGCT polymers which usuallyhave a Mw/Mn of approximately 2 compared to 3 or greater for LLDPE.

A preferred ethylene copolymer is a copolymer of ethylene and a C₁ toC₂₀ alpha olefin. A preferred copolymer is a low modulus ethylene octenecopolymer sold by Dow. This copolymer is formed by Dow'sconstrained-geometry catalyst technology which uses a single sitecatalyst such as cyclo-pentadienyl titanium complexes. As bestunderstood, Dow's constrained geometry catalysts are based on group XVtransition metals that are covalently bonded to a monocyclopentadienylgroup bridged with a heteroatom. The bond angle between themonocyclopentadienyl group, the titanium center and the heteroatom isless than 115°. When the alpha olefin is present in the copolymer in therange of about 10 to 20% by weight, these copolymers are referred to asplastomers. When the percent alpha olefin is greater than 20% thesecopolymers are called elastomers. The preferred ethylene octenecopolymer has the octene comonomer present in an amount less than 25%.Examples of the Dow ethylene octene copolymer have the followingphysical properties.

DENSITY MOLECULAR g/cc WEIGHT MELT MELT MELT Polymer 1. DISTRIBUTIONINDEX FLOW RATIO STRENGTH 0.920 1.97 1.0 9.5 1.89 0.910 1.90 1.0 7.91.68 0.902 2.10 1.0 7.6 1.68

Molecular weight distribution is defined as the ratio of weight averagemolecular weight to number average molecular weight. The lower thefigure, the narrower the molecular weight distribution. Melt flow ratiois defined as the ratio of melt index, as tested with a 10-kg load tothe melt index with a 2-kg load. The higher the ratio, the moreprocessable the material. Melt flow ratio is defined as melt tensionmeasured in grams. The higher the number the greater the melt strength.Other suitable resins are the Exact resins sold by Exxon. Some of theseresins have the following characteristics:

Typical properties of Exact medical grade polyethylenes Value by gradeProperty 4028 4022 4021 4023 4024 4027 Melt index (D1238)* 10 6 22 353.8 4 Density, g./cc. 0.880 0.890 0.885 0.882 0.885 0.895 (D-1505)Hardness (0-2240) Shore A 78 84 84 80 83 89 Shore D 29 35 36 27 35 39Tensile Strength at break, p.s.i. 2220 1700 3260 620 2840 2200 (D-638)Tensile elongation >800 >800 >800 >800 >800 >800 at break, % (D-638)Tensile impact, ft.-lb./sq. in. 145 130 350 280 300 340 (D-1822)Flexural modulus, 5040 4930 3980 3100 4180 7230 p.s.i. (D-790) Vicatsoftening 138 168 158 138 158 181 point ° F.(D-1525) *ASTM test method

The structure of the present invention is comprised of an ethylene,propylene, or styrene polymer or copolymer formed by a polymerizationreaction in the presence of a single site catalyst preferably ametallocene. (The so-formed polymer or copolymer is sometimes referredto herein as the second polymer, for example as the second ethylenepolymer, or as the second propylene polymer, to differentiate it from anethylene or propylene polymer or copolymer that is not so formed, thelatter sometimes being referred to as a first ethylene polymer or afirst propylene polymer.) Ethylene may be copolymerized with anysuitable monomer such as C₃-C₂₀ alpha olefin including propylene,butene-1, 1-pentene, 4-methyl pentene-1, hexene-1 and octene-1. Apreferred comonomer is octene-1. Another preferred comonomer isbutene-1. The preferred ethylene alpha olefin copolymer of the presentinvention has a density in the range of 0.880 gm/cc to about 0.920gm/cc, a more preferred range of 0.890 gm/cc to about 0.915 gm/cc and amost preferred range of about 0.900 gm/cc to about 0.912 gm/cc.

FIG. 1 shows a cross section of a three layer coextruded structure.Layer 14 is the core layer which may be a barrier layer that minimizesthe transmission of oxygen through the structure. Preferred barriermaterials are polyvinylidene chloride copolymers such as copolymers ofvinylidene chloride and vinyl chloride or an alkyl acrylate such asmethyl acrylate. Other preferred barrier materials include ethylenevinyl alcohol, nylon or a metal foil such as aluminum. Layer 14 may alsobe a copolymer of ethylene and styrene formed using a single sitecatalyst in the polymerization reaction. The copolymer of vinylidenechloride may also be polymerized by the polymerization reaction in thepresence of a single site catalyst. In addition, layer 14 may also be apolystyrene formed by a polymerization reaction in the presence of asingle site catalyst. One such polystyrene is the crystallinesyndiotactic polystyrene sold by Idemitsu Petro-Chemical Co., Tokyo,Japan.

On opposite sides of the core layer 14 of FIG. 1 are layers 12 and 16.At least one of these layers 12 is a polymer formed by a polymerizationreaction in the presence of a single site catalyst. The remaining layer16 may be any suitable polymeric material such as a polyester,co-polyester, polyamide, polycarbonate, polypropylene,propylene-ethylene copolymer, ethylene-propylene copolymer, combinationsof polypropylene and ethylene vinyl acetate copolymer, ultra low densitypolyethylene, low density polyethylene, medium density polyethylene,high density polyethylene, linear low density polyethylene copolymers,linear medium density polyethylene copolymer, linear high densitypolyethylene copolymer, ionomer, ethylene acrylic acid copolymer,ethylene ethyl acrylate copolymer, ethylene methyl acrylate copolymer,or ethylene methacrylic acid copolymer.

In an alternate embodiment, the layer 12 may be a blend of a polymerformed by a polymerization reaction in the presence of a single sitecatalyst and a suitable polymeric material such as is identified inconnection with the description of layer 16 above.

As seen in FIG. 2, the structure may also include embodiments which havea fourth layer 28 over the first layer 22 and a fifth polymeric layer 20over the third layer 26. The composition of the fourth layer 28 may beselected from the same group of materials from which the composition ofthe first layer 12 or third layer 16 is selected, and the fifth layer 30may also be the same composition as the first layer 22 or the thirdlayer 26.

In an alternate embodiment of FIG. 2, the five layer structure may havea first layer 28 similar in composition to layer 12 of FIG. 1, i.e., thefilm may have a first layer of a polymer formed by the polymerizationreaction with a single site catalyst or blends thereof with anothersuitable polymeric material. One or both of the second 22 and fourth 26layers may be an adhesive layer.

The composition of adhesive layers 22 and 25 is selected for itscapability to bond the core or barrier layer 24 to the surface layers 28and 30. A variety of the well known extrudable adhesive polymers adherewell to the core or barrier layer 24. Thus, if for example layer 30 is apolypropylene, an adhesive polymer based on polypropylene is desirablyselected for layer 26. Examples of such adhesives are the extrudablepolymers available under the trade designations Admer QF-500, QF550, orQF-551 from Mitsui Petrochemical Company, or Exxon 5610A2.

If the composition of layer 28 or 30 is an ethylene based polymer orcopolymer, an adhesive polymer based on ethylene is preferably selectedfor layer 22, including ethylene homopolymers and copolymers. Such apreferred adhesive composition is an ethylene vinyl acetate copolymercontaining 25% to 30% by weight vinyl acetate. Other ethylene basedhomopolymers and copolymers modified to enhance adhesion properties arewell known under the trade names of, for example, Bynel and Plexar.Typical base polymers for these extrudable adhesives are thepolyethylene and the ethylene vinyl acetate copolymers. Such adhesivepolymers, including the polypropylene-based polymers, are typicallymodified with carboxyl groups such as anhydride. Also acceptable asadhesives are ethylene methyl acrylate copolymers (EMA).

Additional layers may also be present in the structures of the presentinvention. For example, the present invention contemplates 4, 6, 7, 8,and higher numbers of layers in the film of the present invention anddifferent combinations of layer structures may also be present. Forexample, there may be more than one barrier layer, i.e., two layers ofpolyvinylidene chloride copolymers, two layers of foil or two layers ofEVOH or nylon. Alternatively, there may be a layer of EVOH and a layerof a polyvinylidene chloride copolymer or a polyamide or a polystyreneand other combinations of the core materials. The additional layers ofthe present invention also encompass more than one polymer formed by thepolymerization reaction in the presence of a single site catalyst. Thepolymers may be in a layer alone or in the form of a blend. Suitablepolymers for blending with an ethylene polymer formed in apolymerization reaction with a single site catalyst include otherethylene polymers formed in a polymerization reaction with a single sitecatalyst, LDPE, LLDPE, ULDPE, EVA, ionomers, ethylene copolymers,ethylene methyl acrylate (EMA), ethylene acrylic acid (EAA), ethylmethyl acrylic acid (EMAA), propylene polymers, e.g., polypropylene,(PP), ethylene normal butyl acrylate (ENBA), and ethylene propylenecopolymers (PPE). Suitable polymers for blending with a propylenepolymers formed in a polymerization reaction with a single site catalystinclude ethylene propylene copolymers.

Preferred blends using EVA's are those having lower VA content as theytend to yield EVA layers having better hot strength. EVA'S having higherVA content tend to yield EVA layers having increased adhesion to forexample, the vinylidene chloride copolymer layer. EVA's having virtuallyany amount VA will have better adhesion to the vinylidene chloridecopolymer layer than an ethylene homopolymer. However, good interlayeradhesion is considered desirable in the invention, and thus, steps areusually taken to enhance adhesion where no unacceptable negative effectis encountered. Thus, higher VA contents, in the range of 6% to 12*vinyl acetate are preferred, a melt index of less than 1 is alsopreferred. While blend amounts are shown herein in weight percent, VAcontents are mole percent. Especially preferred EVA's have VA content of7% to 9% and melt index of 0.2 to 0.8. Blends of EVA's to make up theEVA component of layers 16 and 18 are acceptable.

The structure of the present invention may be formed by any conventionalprocess. Such processes include extrusion, coextrusion, extrusioncoating, extrusion lamination, adhesive lamination and the like, andcombinations of processes. The specific process or processes for makinga given film which is neither oriented nor cross-linked can be selectedwith average skill, once the desired structure and compositions havebeen determined.

When the structure of the present invention is a film, the film may alsobe oriented either uniaxially or biaxially. Orientation can also be doneby any conventional process for forming multiple layer films A preferredprocess includes the steps of coextrusion of the layers to be oriented,followed by orientation in one of the conventional processes such asblown tubular orientation or stretch orientation in the form of acontinuous sheet, both being molecular orientation processes. The doublebubble technique disclosure in Pahlke, U.S. Pat. No. 3,456,044 issuitable for use in producing the film of this invention. The films mayalso be formed by a tubular water quench process. In this process thefilm may be extruded downwardly as a tube formed by an annular die, andcarried into a water quench tank, generally with a cascade of water onthe outside surface providing initial cooling. The flattened tape iswithdrawn from the quench bath, is reheated (normally in a second waterbath) to its orientation temperature, is stretched in the machinedirection between two sets of rolls that are so rotated as to establisha linear rate differential therebetween, and is simultaneously orientedin the transverse, or cross-machine, direction as an inflated bubbletrapped between the nips of the rolls. In accordance with conventionalpractice the film will usually be cooled by air in the orientation zone.

The film of the present invention may also be oriented and/orcross-linked. The first step is the formation of a multiple layer film.The formation of the multiple layer film, is usually most easilyaccomplished by coextrusion of the desired layers. Other formationprocesses are acceptable so long as the resulting oriented film at theconclusion of fabrication processing is a unitary structure.

The second step is orienting the multiple layer film. One method foraccomplishing orientation is by heating the film to a temperatureappropriate to molecular orientation and molecularly orienting it. Thefilm may then be optionally heat set by holding it at an elevatedtemperature while its dimensions are maintained. The orientation step ispreferentially carried out in line with the first step, which is thefilm formation step of the process.

The third step is subjecting the formed and oriented multiple layerfilm, to electron beam irradiation.

The amount of electron beam irradiation is adjusted, depending on themake-up of the specific film to be treated and the end use requirement.While virtually any amount of irradiation will induce somecross-linking, a minimum level of at least 1.0 megarads is usuallypreferred in order to achieve desired levels of enhancement of the hotstrength of the film and to expand the range of temperature at whichsatisfactory heat seals may be formed. While treatment up to about 50megarads can be tolerated, there is usually no need to use more than 10megarads, so this is a preferred upper level of treatment, the mostpreferred dosage being 2 to 5 megarads.

The third step of subjecting the film to electron beam irradiation isperformed only after the multiple layer film has been formed, and aftermolecular orientation, in those embodiments where the film ismolecularly oriented. It should be noted that, in the irradiation step,all of the layers in the film are exposed simultaneously to theirradiation sources, such that irradiation of all the layers of the filmtakes place simultaneously.

In one embodiment of the process, the second step of orientation may beomitted and the unoriented multiple layer film may be cross-linked byirradiation treatment to produce a cross-linked, unoriented, multiplelayer film.

FIG. 7 shows a cross section of a preferred structure, generallydesignated 32, having two layers. The structure can be or comprise thebody wall 34 of a container, for example, the collapsible dispensingcontainer shown in the form of a tube 36 in FIG. 8. Structure 32 iscomprised of a structure or layer 38 comprising a first ethylenepolymer, and a contiguous structure or layer 40 comprised of a propylenepolymer blended with a second ethylene polymer formed by apolymerization reaction with a metallocene catalyst system, or with asingle site catalyst, preferably a metallocene. The propylene polymer oflayer 40 can comprise homopolymers and copolymers of propylene, such aspolypropylenes, copolymers of propylene and ethylene (includingcopolymers of ethylene and propylene), and propylene terpolymers, forexample, elastomeric terpolymers prepared or derived from unsaturatedmonomers comprising propylene and ethylene. The propylene polymer canalso comprise blends of these polymers. Layer 4 of FIG. 7 is an exampleof layer 1 of Example 24.

The second ethylene polymer of the blend of layer 40 preferablycomprises a copolymer or interpolymer of ethylene. Preferably, theethylene polymer is a copolymer or interpolymer of ethylene and an alphaolefin, especially a C₃-C₂₀ alpha olefin. Preferred copolymers ofethylene and alpha olefins are ethylene butene-1 copolymers,particularly linear ethylene butene-1 copolymers.

The first ethylene polymer of layer 38 can comprise a low, linear low,very low or ultra low density polyethylene, a medium densitypolyethylene, a high density polyethylene, an ionomer, or any suitableblend or combination of such ethylene polymers.

Structure 32 can also be comprised of a first layer of a first propylenepolymer of the type of propylene polymer described above in relation tothe blend of propylene polymer and second ethylene polymer, and a secondlayer comprised of an ethylene polymer as described above in relation tofirst ethylene polymer, blended with a second propylene polymer formedby the polymerization reaction with a metallocene catalyst system orwith a single site catalyst, preferably a metallocene. The secondpropylene polymer can comprise an interpolymer or copolymer of propyleneand an alpha olefin, preferably a C₃-C₂₀ alpha olefin.

While structures or members such as a layer formed of a firstpolyethylene and structures or members such as a layer, or a collapsibledispensing container head formed of polypropylene usually do not adherewell to each other, as will be explained, structure 32, formed of layer38 comprised of an ethylene polymer, and layer 40 comprised of a blendof a propylene polymer and a second ethylene polymer, has goodinterlayer adhesion.

FIG. 8 shows a collapsible dispensing tube 36 comprised of a tubularbody wall 34 joined at its upper end directly to the shoulder 42 of ahead, generally designated 44, having a neck 46 with a dispensingorifice 48. The lower end (not shown) of body wall 34 can be sealed, forexample by being brought together and sealed to itself by heat andpressure in a known manner. Head 44 preferably is comprised of a blendof a propylene polymer and a second ethylene polymer which can be suchas those described above for layer 40 of FIG. 7. Although body wall 34of collapsible dispensing tube 36 can be a single layer comprised of afirst ethylene polymer such as described above for layer 38, as shown inFIG. 9, body wall 34 is a two layer structure such as shown in FIG. 7,wherein layer 38, comprised of the first ethylene polymer, is the innerlayer that is fused or joined directly to, and therefore contiguous tohead 42. Layer 40, comprised of the blend of a propylene polymer and asecond ethylene polymer is the outer layer. As will be explained, goodadhesion is obtained between inner layer 38 and shoulder 42 of head 44.

FIG. 10 shows an alternative embodiment of a collapsible dispensing tubeof the invention, generally designated 50, having a head 52 in turnhaving an integral cap 54 joined or attached to head 50 by an integrallyformed flexible, living hinge 56. Head 52 can be comprised of the samepolymeric material as head 44 of FIG. 8, and body wall 34 can becomprised of the same layers and layer materials as described for FIGS.8 and 9.

The present invention includes improved structures, especially packagingstructures, comprised of a first structure, component or member bondedto a second structure, component or member, preferably contiguously,wherein one of the structures, members or components is comprised of anethylene polymer (sometimes referred to herein as a or the firstethylene polymer), and the other of the structures, components ormembers is comprised of a propylene polymer, and wherein the polymer ofeither structure is blended with and is a blend of a polymer formed bythe polymerization reaction with a metallocene catalyst system, or witha single site catalyst, preferably a metallocene. The so-formed polymercan be an ethylene polymer (sometimes referred to herein as a or thesecond ethylene polymer) which is blended with the propylene polymer ofone of the structures, and/or it can be a propylene polymer (sometimesreferred to herein as a or the second propylene polymer) which isblended with the first ethylene polymer of the other structure. Theinvention is especially concerned with such improved structures,especially packaging structures, wherein the so-formed polymer is asecond ethylene polymer, and it is blended with the propylene polymer ofthe propylene polymer structure. Thus, the present invention includesimproved packaging structures where one of the first or secondstructures, components or members is comprised of a first ethylenepolymer, and the other is comprised of a blend of a propylene polymerand a second ethylene polymer. The improved packaging structures havegood bond strength, and there is no stress cracking between a firstethylene polymer body layer structure and a propylene polymer containeror tube head structure, after the container or tube is exposed to stresscrack-inducing agents. Also, desirable properties provided by thepropylene polymer to its structure, for example, in providingflexibility to an integral living hinge which integrally joins a cap toa tube head comprised of a blend of propylene polymer and the secondethylene polymer, is not diminished as compared to such a tube headcomprised of the propylene polymer without the second ethylene polymer.

The structures of the invention having improved bond strength includeany first structure comprised of a first ethylene polymer and any secondstructure comprised of the blend of a propylene polymer and a secondethylene polymer. The structure can be merely two layers. Preferably,the structure is a packaging structure which can be a container, such asa collapsible dispensing container or tube, or its body wall or head, ora combination of such or other components. Thus, the structure can becomprised of a two layer film, side wall or body wall, wherein one layeris comprised of the first ethylene polymer and the other layer iscomprised of the blend of propylene polymer and second ethylene polymer.The structure can also be comprised of such a two layer body or sidewall or a single layer body or side wall comprised of first ethylenepolymer, where the layer of first ethylene polymer of the single, doubleor multi-layer body wall is joined to a component of the package such asa collapsible dispensing container or tube head comprised of the blendof propylene polymer and second ethylene polymer.

The first ethylene polymer can be an ethylene homopolymer, copolymer,terpolymer or other interpolymer, or it can be a blend of any of suchpolymers. The first ethylene polymer can be an ethylene polymer such asdescribed above in connection with layer 38 of FIG. 7 or 9. These firstethylene polymers are well known and often employed in the packagingindustry. Collapsible dispensing containers or tubes have inner andouter surface layers either or both of which can be bonded to a tubehead. Typically, the inner layer is bonded to the tube head and iscomprised of LDPE, an LLDPE or a blend thereof. First ethylene polymerssuitable for plastic tube extrusion, for lamination or extrusionovercoats, for use as an interior surface layer of collapsibledispensing containers and tubes are well known in the art. Suitablematerials for such uses include LDPE's having a melt index of from about0.10 to about 15.0 g/10 min, and a density of from about 0.910 to about0.940 g/cm³. A preferred LDPE is currently available from Equistar,successor to Millenium Petrochemicals, Inc., under the trade designationPetrothene® NA-980-000, having a melt index of about 0.25 g/10 min and adensity of about 0.920 g/cm³. Suitable LLDPE's for such uses may havesimilar melt index and density characteristics as the aforementionedLDPE's. A suitable first ethylene polymer can be a blend of about 75 wt.% of the above-mentioned LDPE and about 25 wt. % of such an LLDPE.

Propylene polymers which can be employed with the second ethylenepolymers in the blends or structures of the invention, i.e., thosepropylene polymers which are not formed by the polymerization reactionwith a metallocene catalyst system, or with a single site catalyst,include those propylene polymers referred to above in connection withlayer 40 of FIGS. 7 and 9. Suitable propylene polymers are known in theart. Generally, suitable polypropylenes can have a melt index of about0.10 to about 15.0 g/10 min, and a density of from about 0.870 to about0.915 g/cm³. Preferably, the propylene polymer, especially when it is apropylene terpolymer or propylene ethylene copolymer, has a melt flowrate of from about 0.7 to about 6 g/10 min, a density of about 0.870 toabout 0.910 g/cm³ and a DSC melting point of about 161° C.

Propylene polymers suitable for use as a single layer structure, or as alayer of a coextruded two-or-more layered structure, such as of apackaging film or of a body or side wall of a collapsible dispensingcontainer or tube, include extrusion grade, high impact strengthelastomeric propylene terpolymers derived from propylene and ethylene.The terpolymers can be derived from monomers, including, for example,higher olefins and dienes, capable of imparting elastomeric properties,such as improved impact strength, to the terpolymer. The monomers andthe elastomeric propylene terpolymers are known in the art. Preferredpropylene terpolymers include terpolymers of propylene, ethylene and amonomer capable of imparting elastomeric properties to the terpolymer.An example of a preferred extrusion grade, high impact strengthelastomeric propylene terpolymer is available under the tradedesignation Montel KS-021P from Himont Incorporated. Typical propertiesof the terpolymer are a melt flow rate of about 0.9 dg/min (ASTMD-1238), a density of about 0.88 g/cm³ (D792B), an initial hardness(Shore D) of about 48 (D2240) and after 75 seconds, about 38, a tensilestrength at yield (50 mm/min) of about 1.4 K psi (D638), an elongationat yield (50 mm/min) of about 40% (D638), a Flexural Modulus (50 mm/min)of about 55 K psi (D790B), a Notched Izod Impact Strength of“nonbreak-flex” at 73° F. and at −40° F., and of 1.1 at −76° F., and adeflection temperature of about 120° F. at 66 psi. A preferred propylenepolymer suitable for forming a tube head, especially a tube head with aliving hinge as shown in FIG. 10, is Pro-fax 8623, a general extrusionor injection grade high impact strength polypropylene resin. It is acopolymer of about 75 wt. % polypropylene and about 25 wt. %polyethylene. Pro-fax 8623 is available from and is the trademark ofHimont Incorporated. Pro-fax 8623 typically has a melt flow rate ofabout 2 dg/min (D1238), a density of about 0.9 g/cm³ (D792A-2), aRockwell hardness, R scale, of 66 (D785A), a tensile strength at yieldof about 3,000 psi (D638), an elongation at yield of about 12% (D638), aflexural modulus of about 140,000 psi (D790B), a drop weight impactstrength at −20° F. of 44 ft-lbs. (Himont Method), a Notched Izod ImpactStrength at 73° F. of about 12 ft-lb/in, and a deflection temperature at66 psi of about 162° F. (D648). Examples of propylene polymers that maybe suitable for use with second ethylene polymers in the blends andstructures of the invention include polypropylene compositions comprisedof about 60 to 90 parts by weight of polypropylene and about 10 to 40parts by weight of an ethylene/butene-1 polymeric mixture, such as aredescribed in U.S. Pat. No. 4,734,459.

The ethylene polymer that is blended with the propylene polymer, i.e.,the second ethylene polymer, includes the ethylene polymers disclosedabove in connection with layer 40 of FIGS. 7 and 9. The second ethylenepolymer is formed by the polymerization reaction with a metallocenecatalyst system, or with a single site catalyst, for example, ametallocene. The second ethylene polymer can be linear or substantiallylinear. It can be a copolymer of ethylene, preferably a copolymer ofethylene and an alpha olefin, for example a C₃ to C₂₀ alpha olefin,preferably butene-1. More preferably, the second ethylene polymer is alinear ethylene butene-1 copolymer. “Linear” polymers are hereinunderstood to mean that the polymers have no or no detected long chainbranching. “Substantially linear” polymers are disclosed in patentliterature as meaning that the polymer backbone is either unsubstitutedor substituted with up to 3 long chain branches/1000 carbons. Such isherein understood to mean that such polymers have some long chainbranching. The second ethylene polymer can have a melt index of about0.10 to about 15.0 dg/min., preferably about 3.5 to about 4.5 dg/min., adensity of from about 0.880 to about 0.920 g/cm³, more preferably fromabout 0.890 to about 0.915 g/cm³, and most preferably from about 0.900to about 0.912 g/cm³, and a preferred DSC peak melting point of fromabout 92 to about 98° C. Preferred linear ethylene butene-1 copolymersare available under the trade designations Exact™ 3024 and Exact™ 3027from Exxon Chemical. Exact is a trademark of Exxon Chemical. Thesesecond ethylene polymers are produced using Exxon Chemical's EXXPOLtechnology.

TYPICAL PROPERTIES OF EXACT 3024 AND 3027 POLYMERS AND FILMS* ExactExact Method 3024 3027 Units ASTM Polymer Properties Melt Index 4.5 3.5dg/min D- 1238(E) Density 0.905 0.900 g/cm³ D- 792 DSC Peak MeltingPoint 98 92 ° C. Exxon Method Film Properties 1% secant Modulus psiD-882 MD 13100 10100 TD 14300 11500 Tensile Strength at Yield psi D-882MD 870 770 TD 690 620 Tensile Strength at Break psi D-882 MD 6900 8160TD 3960 5210 Elongation at Break % D-882 MD 390 450 TD 660 700 ElmendorfTear Strength g/mil D-1922 MD 180 60 TD 160 200 Dart Drop Impact, F₅₀170 410 g/mil D-1709 Puncture, Force 8.1 7.3 lbs/mil Exxon Method Energy24.1 24.7 in-lbs/mil Total Energy Impact ft-lbs D-4272 At RoomTemperature 0.9 1.2 At −29° F. 0.7 0.7 Haze 0.5 0.4 % D-1003 Gloss 96 98% D-2457 *0.8 mil films produced on a 3.5″ cast film line at 500 ft/mintake-off speed and a melt temperature between 500 and 535° F.

The blend of propylene polymer and a second ethylene polymer cancomprise any suitable minor amount, i.e., less than 50 wt. %, of secondethylene polymer, the remainder being propylene polymer. Preferably, theblend comprises about 5 to about 49 wt. % of second ethylene polymer andabout 51 wt. % to about 95 wt. % of propylene polymer, more preferably,about 70 to about 90 wt. % of propylene polymer, and about 10 to about30 wt. % of second ethylene polymer.

For a two layer film or body wall of a collapsible dispensing tubecomprised of a first layer of first ethylene polymer, preferably theLDPE Petrothene NA-980-000, bonded with good bond strength to a secondlayer of a blend propylene polymer and second ethylene polymerpreferably comprised of the propylene terpolymer Montel KS-021P, theblend preferably is comprised of from about 85 to about 90 wt. % of thepropylene terpolymer, and about 10 to about 15 wt. % of second ethylenepolymer, preferably the linear ethylene butene copolymer Exact 3024. Thefollowing two-layer body wall structures comprised of these materialswere produced:

Example 25

Composition Structure A Layer 1 LDPE - Petrothene NA-980-000 Layer 2Blend of: 90 wt. % Montel KS-012P, and 10 wt. % Exact 3024 Structure BLayer 1 LDPE - Petrothene NA-980-000 Layer 2 Blend of: 85 wt. % MontelKS-021P, and 15 wt. % Exact 3024

The two-layer structures were about 0.018 inch thick, the outer blendlayer being about 30% and the inner LDPE layer being about 70% of thetotal thickness of the structure. The two layer structures were formedby a water quenched tubular coextrusion process during which thecontinuous tubular extrudate was vacuum calibrated by being expanded ina tubular vacuum chamber. The chamber's interior diameter was about 1.5inch. The continuous tubular extrudate was cut into ten (10) tubularbodies, each 5 inches long. The tubular bodies had an internal diameterof about 1.509 inch, an external diameter of about 1.545 inch, and awall thickness of about 0.036 inch. These tubular bodies were suitablefor use as the body wall of a collapsible dispensing tube.

Adhesive Strength Test of Two-layer Structures

The two layer tubular body wall structures shown as Structures A and Bin Example 25 were tested for adhesive or bond strength. Strips ¼ inchwide were cut from the tubular bodies. The strips were mechanically heldat one end and attempts were made at the other end of the strips tomanually peel the outer layer away from the inner layer. While slightdelamination occurred with control strips made from similar strips cutfrom similarly made two-layer coextruded tubular bodies having an outerlayer of 100 wt. % of the propylene terpolymer Montel KS-012P and aninner layer of 100 wt. % of the LDPE Petrothene® NA-980-000, the stripsof the two-layer tubular body wall Structures A and B of the inventionhad good bond strength. Their layers could not manually be pulled apart.

Additional test strips were made of two-layer water quenched coextrudedtubular bodies, i.e., body wall structures, of the invention, thesehaving an outer layer blend of 20 wt. % of the ethylene butene plastomerExact 3024 and 80 wt. % of the propylene terpolymer Montel KS-012P, anda contiguous inner layer of 100% of the LDPE Petrothene® NA-980-000.These were tested as above and found to have good bond strength.However, the latter tubular bodies were less than wholly desirable foruses requiring a smooth outer surface feel, because the exterior surfaceof the outer blend layer of these test strips had a granular surfacefeel when passed against a person's lips.

Similar strips cut from two-layer tubular bodies of the inventionobtained as above but whose outer layer blend contained 30% by weightExact 3024 and the balance Montel KS-012P, were tested and found to havea good bond strength. They had an outer layer surface feel to the lipsthat was worse than those strips having 20% by weight of Exact 3024.

Similar strips obtained from similarly made two-layer tubular bodies ofthe invention having an outer layer blend of about 10 wt. % of secondethylene polymer Exact 3024 and about 90 wt. % of propylene polymerMontel KS-012P, a contiguous inner layer of the LDPE, PetrotheneNA-980-000, and an outer to inner layer thickness ratio is 1:1, weretested and found to have good bond strength and a desirable smooth feelto the outer layer.

From the above tests, it was found that two-layer structures of theinvention having an outer layer of a blend of from about 10 to about 30wt. % of a second ethylene alpha olefin copolymer made from apolymerization reaction with a single site catalyst, and from about 70to about 90 wt. % of a propylene polymer, and having a contiguous innerlayer of first ethylene polymer, had improved adhesive strength ascompared to a two-layer coextruded film having an outer layer of 100%propylene ethylene polymer and an inner layer of a first ethylenepolymer. It was also found that two-layer films of the invention havingan outer layer of from about 10 to less than about 20 wt. % of anethylene butene copolymer made from a single site metallocene catalystand at least 80 to about 90 wt. % of a propylene polymer, and acontiguous inner layer of a first ethylene polymer, had an outer layerwhich for some uses had a more desirable, softer feel than the outerlayer of similar structures having from about 20 to about 30 wt. % ofthe ethylene butene copolymer.

Bond Strength of Tubular Body Walls to Tube Heads

In order to test the adhesive or bond strength of a tubular body wallhaving an inner layer of a first ethylene polymer to a collapsibledispensing tube head made of blend materials of the invention which aredisclosed as comprising the tube head shown in FIG. 8, four sets of suchcollapsible dispensing tube heads were injection molded and, during theprocess, fusion bonded to tubular body walls in a conventional mannerdescribed herein. These unfilled collapsible dispensing tubes weretested for head/body wall bond integrity and stress cracking. For afirst test, four variables of blend materials were used to form theheads. Variables were 1 through 3 were blend materials of the invention.

First Set Of Tube Head Variables And Tests Variables Head Resin Material1 Blend of 70% polypropylene (PP)/30% LDPE* 2 Blend of 80% PP/20% LDPE**3 Blend of 70% PP/30% LDPE** 4 Control: 100% LDPE

The PP of the blends was Pro-fax 8623, a propylene-ethylene copolymercomprising about 75 wt. % PP and about 25 wt. % polyethylene, based onthe weight of the copolymer. The properties of Pro-fax 8623 arepresented above. The LDPE* of the blend of Variable 1 was Exact 3027 andthe LDPE** of the blends of Variables 2 and 3 was Exact 3024, each Exactmaterial being a linear ethylene butene plastomer made from apolymerization reaction using a metallocene single site catalyst whoseproperties are presented above. The LDPE used to form the Control head(Variable 4) is available under the trade designation Rexene 1011 fromHuntsman, Corp. The LDPE of the Control head has a melt flow rate ofabout 1.0 g/10 min (ASTM D1238-E), and a density of about 0.9205 g/cm³(ASTM-D792). The heads which were tested for bond strength and whichwere flex tested had a threaded neck for receiving a threaded cap, asshown in FIG. 8.

Five sample tube heads were injection molded of the material of eachvariable. Sample tubes were made. Each of the sample tube heads wasfusion bonded to a 1⅜ inch diameter extruded single layer LDPE tubularbody wall made of Petrothene NA-980-000, or an LDPE having a melt indexof about 1.2 g/10 min. and a density of about 0.920 g/cm³, availableunder the trade designation LDPE 2020T from E. I. DuPont de Nemours andCompany.

First Head/Body Wall Bond Integrity Test

Each of the tubes made from the five samples of each head variable andof the Control was tested for head/body wall bond integrity. The tubularbodies were fusion bonded to the shoulders of the heads by placing anend of the tubular body in an injection mold and injecting the blend ofpropylene polymer and a second ethylene polymer material into a moldsuch that the end of the LDPE blend inner layer of the body wall wasfused to the shoulder of the tube head. The tubular body walls were cuttransaxially 2 inches from the shoulder. A 2″ long ¼ inch wide strip ofthe body wall was cut from the open end of the transaxial cut edge ofthe body wall up to but not including the shoulder, where the strip wasleft as-bonded to the shoulder. One inch of the strip was clamped intothe top clamp and one inch of the tube body was clamped to the bottomclamp of an Instron tensile strength tester. The load cell of the testerwas 100 KG. With the strip disposed at about 90° to the longitudionalaxis of the tube, the jaws were separated at a rate of about 8 inchesper minute until the strip fractured or separated from the head. PeakInstron tensile strength values are shown in TABLE I below.

TABLE I Variable Instron Tensile Pulls (KG) Average 1 4.88 5.88 4.0 4.363.85 4.6 2 3.57 3.0 2.53 2.24 3.65 3.0 3 5.08 3.97 5.7 4.37 3.87 4.6 45.18 4.93 4.39 627 5.75 5.3.

The Instron test results in TABLE I indicate good head/body wallintegrity for each variable and for the Control. All tubes tested above1.2 KG which was the minimum acceptable value. Strips from all variablesfailed only by eventual fracturing, except for Variable 2 (80% PP/20%LDPE Blend) which had lower tensile values and failed by layer interfaceseparation prior to breakage. The Instron tensile strength values shownin TABLE I are all well above 1.2 KG and, as shown below, are superiorto the values obtainable from attempting to bond the LDPE body walllayer to a tube head made of 100% propylene/ethylene copolymer, withrespect to which no bond was obtained.

Second Set of Tube Head Variables and Test

For a second test, a second set of five variables of blend materialswere used to form a set of tube heads. In this test, Variables 6 through8 were blend materials of the invention.

Variables Head Resin Material 5 Control: 100% PP 6 Blend of 90% PP/10%LDPE* 7 Blend of 80% PP/20% LDPE* 8 Blend of 70% PP/30% LDPE* 9 Control100% HDPE

For the second set of variables, the PP of the blends was Pro-fax 8623and the LDPE* of the blends was EXACT 3027. The propylene polymer (PP)used to form the Control head, Variable 5, was Pro-fax 8623. The HDPEused to form the Control head, Variable 9, was HDPE Alathon M4612available from Equistar Chemicals and having a melt index of about 1.2g/cm³ and a density of from about 0.944 to about 0.948 g/cm³. The headswhich were tested for bond strength had a shoulder, a neck, a cap and aliving hinge that integrally joined the cap to the neck, as shown inFIG. 10.

Six sample tube heads were injection molded of the material of eachvariable. Sample tube heads were made. Each of the sample tube heads wasfusion bonded to a 1⅜ inch diameter extruded single layer tubular bodywall made of the LDPE Petrothene NA-980-000.

Second Head/Body Wall Bond Integrity Test

Each of the tubes made from the six samples of each Variable 5 through 8was tested for head/body wall bond integrity. The tubular bodies werefusion bonded to the shoulders of the tube heads as in the first test,and the same test procedure was employed as the in the first test. PeakInstron tensile strength values are shown in TABLE II below.

TABLE II Variable Instron Tensile Pulls (KG) Average 5 N N N N N N N 6 NN N N N N N 7 1.007 1.5557 1.471 1.098 1.391  .7168 1.207 8 3.350 2.8213.125 2.870 3.799 2.615 3.1  9 2.902 2.819 2.795 2.977 3.122 2.730 2.89 “N” indicates no bond was achieved even with attempts to use variousinjection pressures and temperatures.

The Instron test results in TABLE II indicate that no head/body wallbond was achieved for Variable 5 (Control 100% PP head) and Variable 6(Head blend of 90% PP/10% LDPE*), an average minimally acceptable bondwas achieved for Variable 7 (Head blend of 80% PP/20% LDPE*), and asatisfactory bond was achieved for Variable 8 (Head blend of 70% PP/30%LDPE*). The average bond for Variable 8 was greater than the averagebond for Variable 9 (100% HDPE head).

Head Stress Crack Test

Five collapsible dispensing tubes taken from each of the Variables andfrom the Control of the lot of tubes made and first tested above forhead/body wall bond strength were filled with a solution of 20% Nonox(nonoxynol-9 polyethylene glycol) available under the trade designationIgepal CO-630 from GAF, and 80% ethyl alcohol, in one series of tests,and with a solution of 20% Igepal and 80% water in another series oftests, to chemically accelerate aging of the tube head and body wallmaterials and thereby generate stress cracks at the bonded interface ofthe inner layer of the body wall and the shoulder of the tube head. Thebottom ends of the filled tubes were sealed with clamps and placed andheld in an oven at about 140° F. for various time periods ranging from 3to 19 days. The head stress cracks (HSC) and side stress cracks (SSC)which resulted are shown in TABLE III below.

TABLE III Variables 3 days 7 days 14 days 19 days Using: 20% Igepal/80%Alcohol (HSC/SSC) 1 0/0 0/2 0/1 0/0 2 0/0 0/0 0/1 0/0 3 0/0 0/2 0/0 0/0Control 0/0 0/0 0/2 0/0 Using: 20% Igepal/80% Water 1 0/0 0/0 0/1 0/0 20/0 0/0 0/0 0/0 3 0/0 0/0 0/0 0/0 Control 0/0 0/0 0/0 0/0

Table III shows that no head stress cracks were generated for any of theVariables or for the Control. While some side stress cracks (stresscracks of the tubular body wall) occurred, they were located next to theclamped end seal, well away from the head/body wall bond. These stresscracks are thought to have resulted from the stresses imparted by theend clamps.

Head Hinge Flex Tests

Collapsible dispensing tube heads having a cap integrally joined to thehead by an integral living hinge or strap, as shown in FIG. 10, wereflex tested. The tube heads were injection molded using the samematerials as used for the variable and control materials employed in thefirst head/body wall bond integrity test and in the head stress cracktest. Five tube heads of each variable and of the control were made, andthe cap of each tube was mechanically moved from the open to closed toopen positions (1 cycle) for 10,000 cycles without interruption. Whiletwo of the five control samples exhibited partial fracturing of thehinge, the hinges of all of the variables of the heads weresatisfactory. They showed no signs of failure.

The above tests show that employing a blend of a second ethylenepolymer, preferably an ethylene alpha-olefin copolymer made by apolymerization reaction using a single site catalyst, with a propylenepolymer, preferably a propylene-ethylene copolymer, preferably in rangeof from about 20 to about 30 wt. %, more preferably from about 25 toabout 30 wt. % of second ethylene polymer, with about 70 to about 80 wt.%, more preferably from about 70 to about 75 wt. % of propylene polymer,improves the bond strength of a collapsible tube head to a tubular bodywall inner layer comprised of a first ethylene polymer, for example aLDPE. This is accomplished while maintaining, or without detracting fromthe flexibility or flex endurance through 10,000 open-close cycles of anintegral living hinge of the head, as compared to the living hinge of ahead made of 100% propylene polymer. Thus, a tube body wall layer oranother layer, film or structure comprised of a first ethylene polymercan now be satisfactorily bonded to a layer, tube head or otherstructure made or comprised of a propylene polymer, if the propylenepolymer is blended with a minor amount of a second ethylene polymer madeby a polymerization reaction with a metallocene catalyst system, or witha single site catalyst, which can be a metallocene.

The present invention includes methods for improving the adhesionbetween two packaging structures, for example, between a first structureor layer comprising a first ethylene polymer and a contiguous secondstructure or layer comprising a propylene polymer, or for improving theadhesion between a collapsible dispensing container or tube headcomprised of a propylene polymer and a collapsible dispensing tube bodywall layer comprised of a first ethylene polymer, wherein the methodcomprises blending with the first ethylene polymer which is to form thefirst structure or layer and/or with the propylene polymer which is toform the second structure or layer or the tube head, a polymer formed bythe polymerization reaction with a metallocene catalyst system, or witha single site catalyst, which can be a metallocene. In the method of theinvention, the polymer which is blended can comprise a propylenepolymer, and the propylene polymer is blended with the first ethylenepolymer. Preferably, the polymer which is blended comprises a secondethylene polymer, and the second ethylene polymer, preferably a minoramount, is blended with the propylene polymer which is to form thesecond layer, or the tube head. The amount of the so-formed polymerwhich is blended, is any suitable amount given the materials andstructures involved. The amounts to be blended are disclosed above. Theso-formed polymer can be blended and extruded by conventional means andmethods. For example, pellets of a second ethylene polymer such as Exact3024, can be physically mixed or blended with pellets of the propylenepolymer and fed to a conventional extruder in which the mixture ofpellets is melt blended and coextruded through a tubular die operatedunder standard tube manufacturing conditions well known in the art.

EXAMPLES

Multilayer films may be prepared according to the present invention.Biaxially stretched three layer films may be prepared by a ˜doublebubble” process similar to that disclosed in U.S. Pat. No. 3,456,044 bycoextruding the following compositions through a multilayer die,biaxially stretching the coextruded primary tube. The films may also beirradiated if desired.

Example 1

Layer 1—Copolymer of ethylene and an alpha olefin such as Hexene-1 orOctene-1 formed by the polymerization reaction in the presence of asingle site catalyst or metallocene (hereinafter CEO)

Layer 2—Vinylidene chloride—methyl acrylate (VDC-MA) copolymer

Layer 3—Polyolefin. This film may be biaxally stretched and if necessaryirradiated.

EXAMPLE 2 EXAMPLE 3 EXAMPLE 4 Layer 1 CEO CEO CEO-EVA blend Layer 2VDC-MA VDC-MA VDC-MA Layer 3 ULDPE-EVA blend CEO CEO-EVA blend EXAMPLE 5EXAMPLE 6 EXAMPLE 7 Layer 1 CEO CEO CEO-EVA blend Layer 2 Nylon NylonNylon Layer 3 CEO ULDPE-EVA CEO-EVA blend EXAMPLE 8 EXAMPLE 9 LAYER 1Polyolefin Polyolefin LAYER 2 Styrene copolymer formed Propylenecopolymer By the polymerization reaction formed by the With a singlesite catalyst Polymerization reaction With a single site catalyst LAYER3 Polyolefin Polyolefin EXAMPLE 10 EXAMPLE 11 EXAMPLE 12 Layer 1 CEO CEOCEO-EVA blend Layer 2 CEO EVOH EVOH Layer 3 CEO ULDPE-EVA Blend CEO-EVAblend EXAMPLE 13 EXAMPLE 14 EXAMPLE 15 Layer 1 CEO CEO CEO-EVA blendLayer 2 Tie Tie Tie Layer 3 PVDC Copolymer PVDC Copolymer PVDC Or EVOHor EVOH Copolymer or EVOH Layer 4 Tie Tie Tie Layer 5 EUDPE-EVA BlendCEO CEO-EVA Blend EXAMPLE 16 Layer 1 EVA-ULDPE Layer 2 ULDPE or CEOLayer 3 PVDC Copolymer or EVOH Layer 4 EVA Layer 5 CEO or blend of CEOand EVA

The following examples may also be prepared in accordance with thepresent invention:

Example 17

Meat Film—Forming Web

Formed by TWQ Process

(Tubular Water Quench Process)

LAYER 1 Nylon LAYER 2 Tie LAYER 2 EVOH LAYER 4 Tie LAYERS CEH or CEO

CEH is a copolymer of ethylene and Hexene-1 formed by the polymerizationreaction in the presence of a single site catalyst or a metallocene.Other alpha olefins can be polymerized with the ethylene also.

Example 18-20

Innerliner Films—These films can be formed either on a blown film lineor by using a tubular water quench.

LAYER 1 HDPE LAYER 2 Blend of CEH or CEO and EVA and polybutylene LAYER1 HDPE LAYER 2 CEH or CEO and polybutylene LAYER 1 HDPE LAYER 2 CEH orCEO

Example 21 and 22

Meat—Non Forming Top Web film

LAYER 1 PVDC coated PET LAYER 2 Adhesive (lamination) LAYER 3 CEO or CEH

This film may be formed by adhesive laminating a film formed of acopolymer of ethylene and an alpha olefin with the PVDC coated PET film.

LAYER 1 PVDC coated PET LAYER 2 LDPE - extrusion laminated LAYER 3LDPE/CEH or CEO coextrusion

This film can be formed by extrusion laminating a film of PVDC coatedPET or LDPE.

Example 22

Layer 1—Blend of two or more copolymers of ethylene and an alpha olefinpolymerized in the presence of a single site catalyst or metallocenesuch as CEO with either CEH or CEB. CEB is a copolymer of ethylene andbutene-1 formed by a polymerization reaction in the presence of a singlesite catalyst or a metallocene.

Example 24

Layer 1 Blend of a copolymer of ethylene and an alpha olefin formed by apolymerization reaction in the presence of a single site catalyst or ametallocene with Polyethylene or other polyolefin such as EVA, EMA, EAA,EMAA, ionomers, ENBA, PP or PPE.

The films of example 23 and 24 can either be single layer films or multilayer films where additional layers are present on layer 1.

In the following Examples, two layer structures or films of theinvention were formed and tested for adhesive strength. The outer layerof the film was a blend of about 10% by weight of a propylene polymer,particularly a terpolymer of propylene, butene-1 and an elastomericmonomer, available under the trade designation Montel KS-021P fromHimont Incorporated, and about 90% by weight of an ethylene polymer(sometimes referred to herein as a second ethylene polymer),particularly an ethylene-based butene plastomer, available under thetrade designation Exact 3024 from Exxon Chemical. “Montel” is atrademark of Himont Incorporated, and “Exact” is a trademark of ExxonChemical. The terpolymer Montel KS-021P has a melt flow rate of about0.9 dg/min, (determined by ASTM D-1238), and a density of about 0.88g/cm³ (by ASTM D792B). The ethylene-based plastomer Exact 3024 is madeby a polymerization reaction with a metallocene single site catalyst andtypically has a melt index of about 4.5 dg/min (ASTM D-1238(E)), adensity of about 0.905 g/cm³ (ASTM D-792), and a DSC peak melting pointof about 98° C. (Exxon Method). The inner layer of the film was anethylene polymer, sometimes referred to herein as a first ethylenepolymer, particularly an LDPE under the trade designation Petrothene ®NA-980-000 available from Millenium Petrochemicals, Inc.

The material is available under the trade designation Pro-Fax 8623 fromMontell USA, Inc. The copolymer has a melt flow rate of about 2 (ASTMD-1238), a density of about 0.900 g/mc³ (ASTM D-792A-2) and a DSCmelting point of 161° C. (with a slight peak at 121) a tensile strengthat yield of about 3,000 psi (21 Mpa) (ASTM D638), and an elongation atyield of about 12% (ASTM D638). “Pro-Fax” is a trademark of HimontIncorcorpated.

We claim:
 1. A method for improving the adhesion between a first layercomprising a first ethylene polymer and a contiguous second layercomprising a propylene polymer, which comprises: blending with thepropylene polymer a second ethylene polymer formed by the polymerizationreaction with a single site catalyst, the propylene polymer being anelastomeric terpolymer of ethylene, propylene and a monomer capable ofimparting elastomeric properties to the terpolymer, the second ethylenepolymer being an ethylene butene-1 copolymer, the blend having about 10to about 15% of the terpolymer and about 85 to about 90 wt % of theethylene butene-1 copolymer.
 2. The method of claim 1, wherein thesecond ethylene polymer is a linear ethylene butene-1 copolymer.
 3. Themethod of claim 1, wherein the first ethylene polymer is a low densitypolyethylene.
 4. The method of claim 2, wherein the first ethylenepolymer is a low density polyethylene.
 5. The method of claim 2, whereinthe terpolymer has a melt flow rate of abou 0.9 dg/min and a density ofabout 0.88 g/cm³.